Device for the time-dependent control of the duration of regeneration of an air drier

ABSTRACT

An apparatus for time dependent control of a regeneration time of an air-dryer. The control apparatus has a shutoff valve, which is disposed in a line between a tank that furnishes regeneration air and an air dryer that can be regenerated by the countercurrent method. For the regeneration of the air dryer, the shutoff valve is switched into an open position by a control pressure and is returned to its closing position by spring force counter to a pneumatic delay device which concludes the regeneration. In the pneumatic delay device, air is displaced through a throttle restriction in the form of a permeable membrane, for instance of porous polytetrafluoroethylene. The apparatus for time-dependent control of the regeneration time of an air dryer is intended in particular for compressed air systems of motor vehicles.

PRIOR ART

The invention is based on an apparatus for time-dependent control of theregeneration time of an air dryer.

One such device is already known (European Patent Disclosure EP 0 036569 A1) in which a spring-loaded piston connected to the shutoff valveis displaceable between two cylinder chambers of a cylinder bydifferential pressure. The two cylinder chambers communicate throughthrottle bores of different cross sections and with the interior of theair dryer. The compressed air they contain is used, along with the airtaken from a supply air tank, to regenerate the air dryer. The knownapparatus requires a relatively large amount of installation space.Moreover, the length of the regeneration phase is dependent onconsumerdictated pressure fluctuations in the compressed air system aswell as on production-related differences among the throttle bores.

ADVANTAGES OF THE INVENTION

The apparatus according to the invention is advantageous over the priorart in that the action of the throttle restriction is adjustable to veryclose tolerances. This can be done by modifying the structure of themembrane, or in other words its mean pore diameter, pore volume,effective membrane surface area, and membrane thickness. On thecondition of replicable pressure conditions of the air penetrating themembrane, it is thus possible to attain a very accurate time-dependentcontrol of the regeneration time. The regeneration of the air dryer istherefore controllable without unnecessary consumption of compressedair.

Based on a choice of material consistent performance of the membraneover the service life of the air dryer can be expected, since thematerial is largely resistant and dirt-repellent.

With a refinement of the device not only is the introduction of air intothe hollow chamber achieved, but the sealing off of the piston from thehollow chamber is attained, if the air is positively displaced from thehollow chamber on its way through the membrane.

The embodiment of the invention defined herein is a space-saving way,that is also practical to produce and install, of combining the elementsof the regeneration time control apparatus, which includes the delaydevice, the shutoff valve, and the actuating means.

Further advantages will become apparent from the ensuing description ofthe apparatus according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention is shown in simplified form inthe drawing and is described in further detail in the ensuingdescription.

FIG. 1 shows a circuit diagram of a compressed air system, shown only inpart, with an air dryer, and

FIG. 2 shows a section through an apparatus for controlling theregeneration time of the air dryer.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The circuit diagram in FIG. 1 shows a compressed air system 10,specifically both the energy supply and part of the transmissionequipment of a brake system for utility vehicles. The compressed airsystem 10 has an air compressor 11 with a feed line 12 connected,thereto the feed line has in succession in the feed direction, apressure controller 13, an air dryer 14, a one way check valve 15 and aguard valve 16. A supply tank 17 for compressed air of a consumercircuit, not otherwise shown, is connected to the guard valve 16. Noother consumer circuits of the compressed air system 10 are shown here.

The air dryer 14 is a so-called single-chamber air dryer. It contains adrying medium, with which moisture-laden compressed air pumped by theair compressor 12 and arriving from being distributed to the consumercircuits, is dehumidified. The drying medium absorbs the moisture untilits drying capacity is exhausted; this is why the air dryer 14 requiresregeneration of its drying medium. To that end, an apparatus 20 for thetime-dependent control of the regeneration time of the single-chamberair dryer 14 is provided. The regeneration time control apparatus 20includes a shutoff valve 21, a pneumatic delay device 22, and a throttle23. The shutoff valve 21 is in series with the throttle 23 in ascavenging line 24, which begins at the feed line 12 between the checkvalve 15 and the guard valve 16 and discharges into the air dryer 14.The shutoff valve 21 is a 2/2-way valve, with a closing position as itsbasic position. It can be switched pneumatically into its open positioncounter to the force of an adjustable restoring spring 25. To that end,the shutoff valve 21 is connected to the pressure controller 13 by acontrol line 26. The delay device 22, operatively connected to theshutoff valve 21, is shown as a cylinder 27 with a piston 28, in which acheck valve 29, connecting the two cylinder chambers, and a throttlerestriction 30 are both accommodated. Also shown in the circuit diagramof FIG. 1 are two control lines 31 and 32. The control line 31 begins atthe feed line 12 between the check valve 15 and the guard valve 16 andleads to a control input to the pressure controller 13. The control line32, conversely, extends from a control output of the pressure controller13 and leads to a control input of the air dryer 14, in order to switchthe air dryer into the regeneration mode.

The mode of operation of the regeneration control apparatus 20 is asfollows:

The compressed air pumped by the air compressor 11 is carried, asalready mentioned, through the feed line 12 to the guard valve 16 anddistributed to the consumer circuits. When an upper limit pressure inthe consumer part of the compressed air system 10 is reached, thepressure controller is switched over, via the control line 31. The aircompressor 11 now changes over to the idling mode. With the switchoverof the pressure controller 13, or even during the pumping mode of theair compressor 11, the shutoff valve 21 is switched into its openposition via the control line 26, counter to the force of the restoringspring 25. At the same time, the piston 28 of the delay device isdisplaced in the cylinder 27. In this process, air passes through thecheck valve 29 from one side of the piston 28 to the other side thereof.With the switchover of the pressure controller 13, the air dryer 14 ismoreover switched to the regeneration mode, via the control line 32. Drycompressed air, drawn from the air tank 17, now flows through thescavenging line 24 to the throttle 23, where the compressed air isdepressurized and discharged to the air dryer 14. The dry air is passedin a countercurrent through the air dryer 14 and discharged to theatmosphere. The air in the drying medium absorbs the water that hasaccumulated in the air dryer 14, so that the air dryer is regeneratedthereby, or in other words regains its capacity of extracting themoisture from compressed air pumped to it.

For the duration of the regeneration process, the restoring spring 25seeks to return the shutoff valve 21 to its basic position. The throttlerestriction 30 in the piston 28 of the delay device 22 presentsresistance to such a return, by delaying the return flow of the air fromone side of the piston 28 to the other. After a preselected period oftime determined by a suitable design of the throttle restriction, theshutoff valve switches into its closing position. This concludes theregeneration phase of the air dryer 14. The regeneration time orduration is set such that any unnecessary consumption of compressed airfrom the air tank 17 is avoided and that complete regeneration of theair dryer is attained. If the consumer causes the air pressure in theconsumer circuits of the compressed air system 10 to drop to a lowerlimit value, then the pressure controller is switched over to thefilling position and the air dryer 14 is switched over to thedehumidifying mode. The compressed air pumped by the air compressor 11is dehumidified, as described at the outset, by the regenerated airdryer 14 and discharged to the consumer circuits.

The exemplary embodiment of the regeneration time control apparatus 20shown in FIG. 2 includes a housing 35, in which the throttle 23, shutoffvalve 21 and delay device 22 are combined. The regeneration time controlapparatus 20 may be fitted into the single-chamber air dryer 14.

The cylinder 27 of the delay device 22, embodied in the housing 35, isclosed off by a cylinder cap 36. Coaxially to the piston 28, which isreceived longitudinally movably in the cylinder 27, the cylinder cap 36is penetrated by an adjusting screw 37, on which a spring plate 38 issupported inside the cylinder. Seated on this spring plate is therestoring spring 25, embodied as a helical compression spring, of theshutoff valve 21. The spring 25 engages the piston 28, which divides aspring chamber 39, containing the spring, from a hollow chamber 40 ofthe cylinder 27 that is located above the piston. The prestressing ofthe spring 25 can be varied by means of the adjusting screw 37.

A shaft sealing ring 41 is received on the piston 28, to seal it offfrom the cylinder 27. This sealing ring acts as the check valve 29 shownin the circuit diagram of FIG. 1: Upon the downward stroke of the piston28, air at atmospheric pressure is capable of emerging from the springchamber 39 to reach the hollow chamber 40 on the other side of thecylinder; in the reverse direction, however, this course is blocked bythe shaft sealing ring 41. The piston 28, which acts as an adjustablewall, is in this way bypassed by the check valve 29 whose admissiondirection is into the hollow chamber 28.

The piston 28 has a through bore 44, formed by both an axial bore and atransverse bore, that connects the spring chamber 39 to the hollowchamber 40. A disk 45 of porous polytetrafluoroethylene, which acts asan air-permeable membrane, is received in the through bore 44. Amaterial of this kind is sold by the company doing business as BerghofLabor- und Automationstechnik GmbH, D-72800 Eningen, Federal Republic ofGermany. The membrane acts as the throttle restriction 30, shown in thecircuit diagram of FIG. 1, of the delay device 22. The disk 45 isfastened in the through bore 44 by a bush screw 46. Air in the hollowchamber 40 can take its course into the spring chamber 39 only throughthe disk 45. The resistance that the disk 45 presents to the air isdetermined by the mean pore diameter, the pore volume, the effectivesurface area, and the thickness of the disk 45.

On the side remote from the spring, the piston 28 is provided with astepped piston rod 49. Following a step face 50 that reduces the crosssection, the piston rod 49 is continued with an end portion 51, which onits free end has a closing member 52 of the shutoff valve 21. Theclosing member 52 is supported, in the basic position shown for theshutoff valve 21, on a valve seat 53 toward the housing. On the sidetoward the closing member, a portion of the scavenging line 24discharges into the housing 35; on the side toward the valve, there is abore 54 in the housing 35, and as indicated in the circuit diagram ofFIG. 1 this bore forms the throttle 23 in the portion of the scavengingline 24 leading to the air dryer 14. Also discharging into the housing35 is a portion, communicating with the step face 50, of the controlline 26 that extends from the pressure controller 13. The piston rod 49is sealed off from the housing 35, between the portion of the scavengingline 24 and the portion of the control line 26, by a sealing ring 55. Asecond sealing ring 56 divides the portion of the control line 26 fromthe hollow chamber 40; a third sealing ring 57 between the cylinder cap36 and the cylinder 27 prevents dirt from getting into the springchamber 39, while a fourth sealing ring can be disposed for the samepurpose between the adjusting screw 37 and the cylinder cap.

The regeneration time control apparatus 20 can be made operative asfollows:

By feeding control pressure into the control line 26, a force is exertedon the step face 50 of the piston rod 49 that axially displaces thepiston 28, with the piston rod 49, counter to the force of the spring 25until the piston strikes the cylinder cap 36. In the process, the airlocated in the spring chamber 39 is positively displaced, and onovercoming the shaft sealing ring 41 it reaches the hollow chamber 40,which has been enlarged by the piston motion. At the same time as thedisplacement of the piston 28, the shutoff valve 21 is also switchedfrom the closing position to the open position. As the control pressurefalls away at the step face 50, the restoring motion of the piston 28begins. The restoring force exerted on the piston 28 by the spring 25effects a compression of the air enclosed in the hollow chamber 40,which can pass only through the through bore 44 into the pressurelessspring chamber 39. The throttling action of the polytetrafluoroethylenedisk 45 presents a resistance to this passage of the air; that is, thepiston 28 does not reach its outset position, in which it closes theshutoff valve 21, until after a certain period of time. This length oftime, which determines the regeneration time, can be varied not only byhow the disk 45 is embodied, but also by adjusting the prestressing ofthe spring 25 by means of the axially adjustable adjusting screw 37.Moreover, the volume of the hollow chamber 40 can also be used to varythe regeneration time setting.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. An apparatus (20) for time-dependent control of aregeneration time of an air dryer (14), for compressed air systems (10)of motor vehicles, comprising a shutoff valve (21), disposed in a line(24) between an air tank (17) containing compressed air and the airdryer (14), which for the regeneration of the air dryer (14) is switchedinto an open position by a control pressure and is returned by springforce counter to a pneumatic delay device (22) to a closing positionthat concludes the regeneration, wherein air is displaced through athrottle restriction (30) in the pneumatic delay device (22),thethrottle restriction (30) is formed by a permeable membrane or disk(45).
 2. An apparatus of claim 1, in which the membrane or disk (45)comprises porous polytetrafluoroethylene (PTFE).
 3. An apparatus ofclaim 1, in which the membrane or disk (45) is disposed in a throughbore (44) of a displaceable wall (28) of the delay device (22), saidwall (28) on one side defines a hollow chamber (40) and on another sideis under the influence of a compression spring (25).
 4. An apparatus ofclaim 3, in which the displaceable wall (28) is movable by the controlpressure counter to a force of the compression spring (25) into aposition that enlarges the hollow chamber (40).
 5. An apparatus of claim4, in which the displaceable wall (28) is bypassed by a check valve (29)with an admission direction into the hollow chamber (40).
 6. Anapparatus of claim 5, in which the displaceable wall (28) comprises apiston (28) in a cylinder (27) and has a shaft sealing ring (41) thatacts as a check valve (29).
 7. An apparatus of claim 6, in which thepiston (28) has a stepped piston rod (49), whose end portion (51) remotefrom the spring has a closing member (52) of the shutoff valve (21),while one step face (50) of the piston rod (49) forms an action face forthe control pressure.
 8. An apparatus of claim 7, in which thecompression spring (25) is seated with a face end remote from the pistonon a spring plate (38) that is axially adjustable.